1. Field of the Invention
The present invention relates to a new and improved device for handling reagent strips and the like in quantitative measurement instruments; and, more particularly, to a new and improved slide mechanism for portable reflectance photometers moved by positive snap action to one of two positions thereby providing simplified operation.
2. Description of the Background Art
Devices that measure fluctuations in a person's blood sugar, or glucose levels have become everyday necessities for many of the nation's seven million diabetics. Because this disorder can cause dangerous anomalies in blood chemistry and is believed to be a contributor to vision loss and kidney failure, most diabetics need to test themselves periodically and adjust their glucose count accordingly, usually with insulin injections. Patients who are insulin dependent--about 10% to 15% of diabetics--are instructed by doctors to check their blood-sugar levels as often as four times daily.
For years the solution for diabetics was one of several urinanalysis kits that, despite repeated improvements, provided imprecise measurements of glucose in the blood. Examples of early urine testing for glucose are described in U.S. Pat. Nos. 2,387,244 and 3,164,534. Later, reagent strips for urine testing were developed. Testing of urine for glucose, however, is limited in accuracy particularly since the renal threshhold for glucose spillage into the urine is different for each individual. Moreover, sugar (glucose) in urine is a sign that the glucose was too high several hours prior to the test because of the time delay in glucose reaching the urine. Readings taken from the urine, therefore, are indicative of the glucose level in the blood several hours before the urine is tested.
More accurate readings are possible by taking readings directly from blood to determine current glucose levels. Proper dosages of insulin are more obtainable by increasing the frequency of taking the reading. For these reasons, the advent of home blood tests is considered by some to be the most significant advance in the care of diabetics since the discovery of insulin in 1921. Home blood glucose testing was made available with the development of reagent strips for whole blood testing. The reagent strip includes a reactant system comprising an enzyme, such as glucose oxidase, capable of catalyzing the oxidation reaction of glucose to gluconic acid and hydrogen peroxide; an indicator or oxidizable dye, such as o-tolidine; and a substance having peroxidative activity capable of catalyzing the oxidation of the indicator. The dye or indicator turns a visually different shade of color and the shade is an indication of the glucose level. For an accurate reading of the glucose level, a reflectance photometer can be used.
Reflectance photometers measure the degree of color developed on a reagent strip by the glucose contained in a drop of whole blood. The photometer includes a light source. Light emitted by the light source strikes a calibration chip in the instrument providing a first signal used to calibrate the photometer. The calibration step is followed by the light source again emitting light that strikes the reagent area on the reagent strip. Light is reflected into the instrument and is converted to a second electrical signal. A microcomputer computes the first signal to calibrate the instrument and converts the second signal into a direct blood glucose value. This information is displayed digitally.
In order for reflectance photometers to be used by diabetics and other non-technical users, it is important that a user can conveniently calibrate the instrument, load a reacted reagent strip, move the reacted reagent strip into position for reading and read the digital display. It is desirable to provide positive action of the mechanism that calibrates the instrument, loads a reagent strip and reads the reagent strip. This positive action minimizes the possibility for user error. It is also useful to allow for cleaning of those components of the instrument that can become contaminated with patient sample.
To increase the ease of carrying the instrument, thereby allowing more frequent use and helping to control insulin requirements, reflectance photometers are being made smaller and less expensive. Portability also requires an inexpensive and simplified procedure for blocking the leakage of ambient light around the reagent area of the reagent strip during measurement. This ambient light can result in an inaccurate reading by the instrument. It is desirable to provide a low cost component for the instrument that will seal out ambient light from the reagent area during measurement by the instrument.